Dipeptidyl Peptidase IV (DPP-4) (also known as CD26 or adenosine deaminase binding protein) is a type II transmembrane serine protease in the prolyl oligopeptidase family that catalyzes the hydrolysis of N-terminal dipeptides from the N-terminus of polypeptides having a proline or alanine in position 2 (Enzyme Commission (EC) Number 3.4.14.5 (BRENDA I IUBMB)). A number of chemokine and peptide hormones including GLP-1, GLP-2, gastric inhibitory polypeptide (GIP), pituitary adenylate cyclase-activating polypeptide (PACAP) and neuropeptide Y are cleaved and inactivated by DPP-4. See, e.g., Yaron A., Naider F. Crit. Rev. Biochem. Mol. Biol. 28, 31-81 (1993); Mentlein R. Regul Pept. 85(1):9-24 (1999). As a result, DPP-4 regulates glucose metabolism, appetite and pain regulation though its ability to inhibit chemokine and peptide hormones.
In addition to its role as a regulatory protease, DPP-4 also binds several molecules and induces intracellular signal transduction. In particular, DPP-4 induces T-cell co-stimulation/proliferation and lymphocyte-epithelial cell adhesion by binding to several ligands including adenosine deaminase (ADA). See, e.g., Gines et al., Biochem. J. 361:203-209 (2002). DPP-4 has also been reported to enhance T-cell maturation and migration, cytokine secretion, antibody production, immunoglobulin isotype switching of B cells, and activation of cytotoxic T cells. Ohnuma et. al., Front Biosci. 13:2299-310 (2008).
DPP-4 is a 110 kDa glycoprotein, encoded by a gene located on chromosome 2 (2q24.3) (Abbott et al. Immunogenetics. 40(5):331-8 (1994)), and functions as a homodimer consisting of 766 amino acids. Each monomer consists of two domains: an alpha/beta hydrolase domain and an eight-blade beta-propeller domain. DPP-4 is widely expressed in several tissues including liver, lung, kidney, epithelial cells and lymphocytes. Heike et al. Clin Exp Immunol. 74:431-434 91988); Gorrell et al., Scand J Immunol. 54:249-264 (2001). Upon T cell activation, DPP-4 expression is up-regulated on resting T cells. A soluble, active form of DPP-4 containing most of the extracellular domain (residues 39-766) including the key catalytic domain, has also been observed. Ikushima H, et al. Cell Immunol. 215(1):106-10 (2002).
DPP-4 gene knock out mice show improved glucose tolerance with oral glucose loading, increased insulin and GLP-1 activity; resistance to diet-induced obesity; and increased insulin sensitivity following high-fat diets. Marguet et al., Proc Natl Acad Sci USA. 97(12):6874-9 (2000); Conarello et al., Proc Natl Acad Sci USA. 100(11):6825-30 (2003). In addition to its role in metabolic disorders and glycemic control, DPP-4 has also been implicated in controlling immune function, cell migration, entry of viruses into cells, cancer metastasis and inflammation. See, e.g., Aytac et al., Curr Drug Targets Immune Endocr Metabol Disord 4(1):11-8 (2004).
More recently, DPP-4 expression has been reported to be highly induced by Interleukin-13 (IL-13). See, e.g., Zhang et al., Am J Respir Crit Care Med 189:A4875 (2014); Shiobara et al., Am J Respir Crit Care Med 189:A4239 (2014); Brightling et al., Am J Respir Crit Care Med 189:A6670 (2014); U.S. Provisional Application No. 61/931,878, filed Jan. 27, 2014; and U.S. Provisional Application No. 61/990,932, filed May 9, 2014, each herein incorporated by reference in its entirety for all purposes. IL-13 is a 114 amino acid cytokine with an unmodified molecular mass of approximately 12 kDa. McKenzie, A. N., et al. J Immunol, 1993. 150:5436-44; Minty, A., et al. Nature, 1993. 362:248-50. IL-13 levels have been shown to correlate with disease severity in a number of diseases or disorders including, but not limited to, asthma, chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, and atopic dermatitis. For example, in asthmatics and rodent models of allergic inflammation elevated IL-13 levels have been reported to correlate with disease severity (see U.S. Pat. Appl. Publ. No. 2012-0052060, published Mar. 1, 2012, and incorporated herein by reference in its entirety).
Chronic obstructive pulmonary disease (COPD) includes patient populations with varying degrees of chronic bronchitis, small airway disease, and emphysema, and is characterized by progressive irreversible lung function decline that responds poorly to current asthma based therapy. Zheng et al (J Clin Invest, 2000. 106:1081-93) demonstrated that overexpression of IL-13 in the mouse lung caused emphysema, elevated mucus production, and inflammation, reflecting aspects of human COPD. The signs are therefore that IL-13 plays an important role in the pathogenesis of COPD, particularly in patients with asthma-like features.
IL-13 can also play a role in the pathogenesis of inflammatory bowel disease, and has been associated with fibrotic conditions, such as idiopathic pulmonary fibrosis (IPF). See, e.g., Jovani, M., et al. Curr Drug Targets. 2013.12:1444-52; and Rafii, R., et al. J Thorac Dis. 2013. 1:48-73
Atopic dermatitis is a common chronic inflammatory skin disease that is often associated with other atopic disorders such as allergic rhinitis and asthma (Bieber, New England Journal of Medicine, 2008, 358: 1483-1494). Upregulation of IL-13 mRNA has been observed in subacute and chronic lesions of atopic dermatitis (Tazawa et al., Arch. Dermatol. Res., 2004, 295:459-464; Purwar et al, J. Invest. Derm., 2006, 126, 1043-1051; Oh et al., J Immunol., 2011, 186:7232-42).
Elevated DPP-4 levels have been observed in asthma, COPD and AD patients (see, e.g., U.S. Provisional Application No. 61/931,878, filed Jan. 27, 2014; and U.S. Provisional Application No. 61/990,932, filed May 9, 2014, each incorporated herein by reference in its entirety). In addition, in a phase 2B clinical study involving asthma patients, high serum DPP-4 levels predicted improved response rates in patients treated with an IL-13 antibody antagonist (tralokinumab) identifying DPP-4 as a predictive biomarker for IL-13-mediated disease or disorders including an IL-13-mediated pulmonary disease or disorder (e.g., asthma, IPF or COPD) or an IL-13-mediated chronic inflammatory skin disease or disorder (e.g., atopic dermatitis). See Brightling et al., Am J Respir Crit Care Med 189:A6670 (2014); and U.S. Provisional Application No. 61/931,878, filed Jan. 27, 2014; and U.S. Provisional Application No. 61/990,932, filed May 9, 2014, each herein incorporated by reference in its entirety. Thus, while increased DPP-4 levels are known to correlate with certain IL-13-mediated diseases or disorders and DPP-4 serum levels are known to predict patient response to anti-IL-13 therapy, there remains a need for specific and sensitive assays to measure the amount and/or determine changes in DPP-4 levels in patients, including, but not limited to, patients suffering from an IL-13-mediated disease or disorder. Although there are commercially available reagents which could be used to measure serum DPP-4 levels in patients, these commercially available reagents or kits rely on polyclonal antibodies, which not only introduce assay variations due to lot to lot differences and/or are not very sensitive. Accordingly, there still remains a need for specific and sensitive antibodies, reagents and/or immunoassays to measure the amount and/or determine changes in DPP-4 levels in patients.